Synthesis, thermoanalytical and spectroscopic characterization of newly synthesized macrocyclic complexes of thallium(III) and tin(IV)

Article abstract of DOI:10.1007/s10973-017-6531-x

Abstract: Spectroscopic, thermal and fluorescence properties of various thallium and tin complexes, X-Tl(III)t(4-Y)PP and X-Sn(IV)t(4-Y)PP where X?=?5-SO₃H-2-OHOC₆H₄,(5-SSA); 5-Cl-2-OHOC₆H₄,(5-CSA); and 5-NH₂-2-OHOC₆H₄,(5-NSA) and Y?=?–Cl, –OCH₃, are investigated in detail. Analysis of the spectral data [IR, UV–Vis and NMR (¹H and ¹¹⁹Sn)] of complexes suggests that the two trans-axial ligands are strongly bound in a symmetric manner at the tin center in these complexes. Whereas the absorption and emission studies of thallium complexes characterized the sitting-Atop (SAT) feature of the complexes, the fluorescence lifetime of the tin complexes is found to be higher than thallium complexes. The structure and morphology of complexes were studied by X-ray powdered diffraction analysis. From the X-ray diffractograms, it could be revealed that the complexes are crystallized in mixed crystalline forms. Thermal studies of these porphyrins were carried out in an argon atmosphere from room temperature to 800?°C using thermal analyzer. Evaluation of the thermal analysis of the two metal complexes reveals that the tin(IV) porphyrin complexes are more stable than thallium(III) complexes. Some of the synthesized complexes of thallium and tin have been screened for biological activity against B. subtilis, M. luteus, S. aureus, P. florescens and E. coli by agar well diffusion methods that were found to be inactive against bacterial strains. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10973-017-6531-x

J Therm Anal Calorim
DOI 10.1007/s10973-017-6531-x
Synthesis, thermoanalytical and spectroscopic characterization
of newly synthesized macrocyclic complexes of thallium(III)
and tin(IV)
Sapna Katoch1 Gauri D. Bajju1 Gita Devi1 Altaf Ahmed1
•
•
•
Received: 2 November 2016 / Accepted: 4 June 2017
´
´
Ó Akademiai Kiado, Budapest, Hungary 2017
Abstract Spectroscopic, thermal and fluorescence proper-
ties of various thallium and tin complexes, X-Tl(III)t(4-Y)PP
and X-Sn(IV)t(4-Y)PP where X = 5-SO3H-2-OHOC6
H4,(5-SSA); 5-Cl-2-OHOC6H4,(5-CSA); and 5-NH2-2-
OHOC6H4,(5-NSA) and Y = –Cl, –OCH3, are investigated
in detail. Analysis of the spectral data [IR, UV–Vis and NMR
(1H and 119Sn)] of complexes suggests that the two trans-
axial ligands are strongly bound in a symmetric manner at the
tin center in these complexes. Whereas the absorption and
emission studies of thallium complexes characterized the
sitting-Atop (SAT) feature of the complexes, the fluores-
cence lifetime of the tin complexes is found to be higher than
thallium complexes. The structure and morphology of
complexes were studied by X-ray powdered diffraction
analysis. From the X-ray diffractograms, it could be revealed
that the complexes are crystallized in mixed crystalline
forms. Thermal studies of these porphyrins were carried out
in an argon atmosphere from room temperature to 800 °C
using thermal analyzer. Evaluation of the thermal analysis of
the two metal complexes reveals that the tin(IV) porphyrin
complexes are more stable than thallium(III) complexes.
Some of the synthesized complexes of thallium and tin have
been screened for biological activity against B. subtilis, M.
luteus, S. aureus, P. florescens and E. coli by agar well dif-
fusion methods that were found to be inactive against bac-
terial strains.
Graphical Abstract
OH
C
O
X
O
N
N
Sn
N
N
N
N
Tl
N
N
X
Chemical structure of X-Tl(III)t(4-Y)PP
Chemical structure of X-Sn(IV)t(4-Y)PP
X= 5-SO3H-2-OHOC6H4,(5-SSA); 5-Cl-2-OHOC6H4,(5-CSA); and 5-NH2-2-OHOC6H4,(5-NSA)
Keywords Fluorescence Á Lifetime Á Spectral properties Á
Thermal studies Á XRPD
& Gauri D. Bajju
gauribajju@gmail.com
1
Department of Chemistry, University of Jammu,
Jammu 180006, India
123

S. Katoch et al.
position, which is the only position available, and enables us
to investigate the effects of axial ligand coordination.
Herein, we wish to report on a family of thallium and tin
porphyrins that binds the axial ligands strongly enough to
be isolable in the solid state and also to scrutinize the effect
of axial ligand coordination on the electronic structure and
geometry of the macrocycles. This objective has been
achieved successfully by using 5,10,15,20-p-substituted
tetraphenyl porphyrins (tx-H2TPP,x –Cl, –OCH3) as a
porphyrin macrocycle. The presence of four bulky groups
at the meso-positions severely distorts the porphyrin
geometry and provides an interesting modulation of the
macrocycle properties. We also investigate the effects of
the macrocycle deformations on the metal centers in order
to understand the effects of similar distortions in biology
and their thermal stability.
Introduction
The current interest in coordination chemistry of synthetic
macrocycles increases from the facts that among the most
important biological compounds are those that contain
metal ions with the naturally occurring macrocycles, e.g.,
porphyrins, the chlorophylls and the corrins [1]. Being one
of the vital molecules in many biological processes, poly-
dentate ligand porphyrins and their metalloderivatives have
been artificially synthesized, in part associated with mim-
icking the unusual spectral, redox, kinetic and/or thermo-
dynamic behavior commonly displayed by nature’s
macrocycles [2] and also for the development of new
macrocyclic systems for use in medicine, metal-ion dis-
crimination, metal-ion catalysis, organic synthesis and
analytical processes [3–5]. The thermal and chemical sta-
bility of metalloporphyrins make them attractive building
blocks for the molecular engineering of microporous (i.e.,
˚
pores with diameters less than 20 A) framework solids [6]
Experimental
Material
which also often show enhanced resistance to degradation,
high thermal stabilities and inertness to acids and alkalis
when compared with their metal-containing open-chain
analogs.
The high-purity reagents were commercially purchased
from Merck (SnCl2Á2H2O), Acros organics Tl(OAc)3,
Himedia (p-methoxy benzaldehyde, p-chlorobenzaldehyde)
and were used as received without further purification.
Tin porphyrins are significant and historically important
compounds, for their remarkable combination of chemical
and spectroscopic properties, as well as for their numerous
practical applications, in medicine [7] and in catalysis [8].
Tin(IV) porphyrins have been extensively studied in
biomedical and photocatalytic applications, including split-
ting of water for the production of hydrogen. They are very
stable, easy to synthesize, diamagnetic and usually six-co-
ordinated with trans-diaxial ligands [9]. Although the
chemistry of a wide variety of metalloporphyrins has been
studied in detail, thallium(III) porphyrins have received little
attention. Thallium, being heavy metal, imparts several
properties of interest in porphyrin macrocycle receiving
nowadays a considerable interest as active materials for OL
(optical linear) devices for their capability of absorbing
intense radiations (in the order of several megawatts per
square meter), in the VIS/NIR spectral range in a reversible
fashion with no severe modifications of their optical and
chemical properties [10]. The nonplanar distortions of tetra-
pyrroles that occur naturally in proteins can be induced in
model porphyrins by substantial steric crowding at the
periphery and by inserting heavy metals like thallium(III)
into the core [11]. These distortions have been shown to
modulate the photophysical and chemical properties of the
chromophores and are believed to be responsible, at least in
part, for the various functions and reactivity of chemically
similar tetrapyrrole pigments found in nature. This state of
development has prompted us to synthesize thallium por-
phyrins that easily bind various O/Ndonor ligands to the sixth
Instrument
UV–visible spectra were recorded on UV/VIS spec-
trophotometer model T90 and UV-2600 spectrophotometer
Shimadzu in the range 350-700 nm using 10-4 and 10-5
M
concentrations for each porphyrin and their corresponding
metallated and axially ligated complexes. Infrared analysis
of solid porphyrins was recorded on PerkinElmer-spectrum
400 FTIR spectrophotometer using KBr pellets in the range
of 4000–400 cm-1. The 1H NMR spectra were recorded on
a Bruker Avance II 400 N (400 MHz) using tetramethyl-
silane as internal standard and CDCl3 as a solvent. 119Sn
NMR and 204Tl spectra were recorded on a Bruker
400(L) MHz spectrometer instrument using tetramethyl tin
and TlIII(NO3)3, respectively, as standard using CDCl3 as
solvent. TG and DTA were recorded on thermal analyzer,
PerkinElmer, model STA-6000 using dry samples at the
heating rate of 10 °C min-1 in an argon atmosphere from
room temperature to 900 °C. The phase and size of the as-
prepared samples were determined from powder X-ray
diffraction (XRPD) using D8 X-ray diffractometer (Bru-
ker) at a scanning rate of 12 °C min-1 in the 2h range from
10° to 70°, with Cu Ka radiation (k = 0.15405 nm). The
photoluminescence emission spectra were recorded at
room temperature using Agilent Cary Eclipse fluorescence
123

Synthesis, thermoanalytical and spectroscopic characterization of newly synthesized…
General synthesis of dihydroxoporphyrinatotin(IV)
[SnP1, SnP2]
spectrophotometer equipped with xenon lamp as the exci-
tation source. Lifetime of luminescent nanospheres was
measured from fluorescence lifetime measuring system
Horiba, Model no: Delta Flex-01-NL.
A sample of porphyrin (59 lmol) was dissolved in 10 mL
of chloroform in a one-neck round bottom flask. The
solution of SnCl2Á2H2O (0.59 mmol) in 10 mL of ethanol
was added to it, and the reaction mixture was stirred at
refluxing temperature. The porphyrin solution turned
green on addition of SnCl2Á2H2O. The progress of the
reaction was monitored by TLC analysis and absorption
spectroscopy. The metallation was completed in 4 h as
judged by absorption spectroscopy. Triethylamine
(0.5 mL) was added to the reaction mixture, and the
reaction mixture was stirred for an additional 5 min. The
solvent was removed on rotary evaporator, and crude
compound was subjected to alumina column chromato-
graphic purification. The residual unreacted free-base
porphyrin was collected first with CH2Cl2, and the desired
dihydroxoporphyrinatotin(IV) was eluted with CH2Cl2/
1–2% CH3OH. The solvent was removed on rotary
evaporator and afforded the pure Sn(IV) porphyrin as
purple solid [10].
Synthesis and spectral data of ligands and complexes
5,10,15,20-meso-tetra(p-methoxyphenyl) porphyrin [H2t(p-
OCH3)PP], P1
4-Methoxybenzaldehyde (0.004 mol) was added to 12 mL
of propionic acid. Pyrrole (0.004 mol) was added slowly to
the above refluxing mixture. The reaction mixture was
refluxed for 40 min and then cooled to the room temper-
ature. The purple precipitation was filtered off and washed
with a minimal amount of methanol and then dried. The
material was dissolved in a minimal amount of chloroform
and chromatographed on a column of basic alumina using
chloroform as the eluant. The first band is pink which
contains pure P1. The material was collected and taken to
dryness under vacuum on a rotary evaporator.
5,10,15,20-meso-tetra(p-chlorophenyl) porphyrin [H2t(p-
Cl)PP], P2
Synthesis of axially ligated Tl(III) porphyrins:
XTl(III)t(4-Y)PP [X: different salicylates]
4-Chlorobenzaldehyde (0.004 mol) was added to 12 mL of
propionic acid. Pyrrole (0.004 mol) was added slowly to
the above refluxing mixture. The reaction mixture was
refluxed for 40 min and then cooled to the room temper-
ature. The purple precipitation was filtered off and washed
with a minimal amount of methanol and then dried. The
material was dissolved in a minimal amount of chloroform
and chromatographed on a column of alumina using
chloroform as the eluant. The first band is pink which
contains P2. The material was collected and taken to dry-
ness under vacuum on a rotary evaporator.
(OH)(H2O)Tl(III)t(4-Y)PP 0.15 mmol in 30 mL CHCl3
was treated with respective salicylates 0.56 mmol in
25 mL CH3OH and stirred under reflux for 12 h. After
concentration, the mixture was dissolved in minimum
quantity of CH2Cl2 and extracted four times with distilled
water to remove excess unreacted salicylates. The
resulting solution was then filtered through anhydrous
Na2SO4 in order to remove water molecule. The CH2Cl2
layer was then concentrated to dryness, producing purple
prism. The same procedure was applied for the synthesis
of all axially ligated complexes of thallium porphyrins.
Synthesis of aquo-meso-(5,10,15,20-
tetraarylporphyrinato)thallium(III)hydroxide,
(OH)(H2O)Tlt(4-Y)PP] [Y: –OCH3, –Cl]
[TlP1,TlP2]
Synthesis of axially ligated Sn(IV) porphyrins:
Sn(IV)(X)2t(4-Y)PP [X: different salicylates]
A mixture of porphyrins 0.0068 mmol in CH2Cl2 (10 mL)
and Tl(OAC)3 0.12 mmol in MeOH (2.5 mL) was refluxed
for 1 h. After concentration, the residue was dissolved in
CHCl3, dried with anhydrous Na2SO4 and filtered. The fil-
trate was concentrated and recrystallized from CH2Cl2–
MeOH (1:5 v/v) yielding purple solid of complex
(0.037 mmol, 55%) which was again dissolved in CH2Cl2-
ether (1:1 (v/v)] and layered with MeOH to get purple
crystals of thallium(III) porphyrins.
Trans-dihydroxo(meso-tetraphenylporphyrinato)tin(IV)
(0.13 mmol) prepared above and salicylates (0.26 mmol)
were dissolved in anhydrous CH2Cl2 (20 mL).The reac-
tion mixture was stirred at room temperature. After 24 h,
the solution was filtered through filter paper. The solvent
of the filtrate was evaporated under reduced pressure to
give a crude product. It was then recrystallized from
CH2Cl2/CH3CN solution to afford crystalline solids of
the desired compound.
123

S. Katoch et al.
Table 1 Absorption data of free base, metallated porphyrins and
axially ligated porphyrins
Results and discussion
Ultraviolet studies
B-band
max/nm
Q-bands
kmax/nm
k
The absorption spectral data of all the p-substituted por-
phyrin, its metal complexes and corresponding axially
ligated complexes in methanol are summarized in Table 1.
Both the Soret and Q-bands of the two p-methoxy-
substituted porphyrins are red-shifted compared with p-
chlorophenylporphyrin. The broadening and red shifting of
the absorption bands are usually an indicator of mixing
with the intramolecular charge-transfer character in p–p*
absorption bands. Further, the metallated and axially liga-
ted complexes in case of thallium complexes also exhibited
prominent red shift in their spectra according to the larger
out of plane distance in the case of TlP2 and even the
axially ligated complexes resulting in the higher distortion
of the porphyrin ligand. According to our observations
from the literature, these spectral features are unambigu-
ously characteristic for OOP or SAT complexes, confirm-
ing the expectations based on the size (95 pm ionic radius)
of Tl(III) ion [12, 13]. Whereas in case of tin complexes,
there is a marginal red shift in the absorption spectrum of
SnP2 as well as in the axially ligated derivatives in
methanol media.
P1
418
413
426
424
436
434
434
433
436
433
422
420
427
426
428
427
516, 546, 590, 648
511, 543, 586, 647
526, 562, 596
519, 554, 594
568, 669
P2
TlP1
TlP2
5-SSATlP1
5-SSATlP2
5-CSATlP1
5-CSATlP2
5-NSATlP1
5-NSATlP2
SnP1
563, 671
562, 663
560, 659
563, 660
562, 659
558, 598
SnP2
557, 596
5-SSASnP1
5-SSASnP2
5-CSASnP1
5-CSASnP2
562, 652
561, 650
562, 657
560, 649
ligated complexes also showed the band corresponding to
the OH group giving confirmation that ligation occurs
through COO group in both metal complexes.
IR spectra
NMR studies
The characteristic infrared absorption bands of the free
ligands and four complexes are illustrated in Table 2. All the
free ligands exhibited very sharp peak at 3315–3317 cm-1
indicating the presence of NH group which is found absent
in the corresponding metalloporphyrins. The bands observed
at 3640–3643 cm-1 corresponds to the stretching vibration
of OH groups at the axial position in the metalloporphyrins
[14], and the aromatic C–H appears at 3055 cm-1. The
symmetric (tsym) and asymmetric (tasym) COO bands
observed at 1583 and 1479 cm-1 in tin complexes bound in
the unidentate mode and shift to the lower frequency when
compared to the free ligand [15].The bands in the region
1720–1724 cm-1 are assigned to the C=O group of salicy-
lates in thallium complexes. The band at 1606 and
1633 cm-1 is assigned to the asymmetric vibration of C=O
bond in the bidentate mode of salicylates in thallium com-
plexes [16]. The band appearing at 1463 cm-1 is assigned to
the symmetric (tsym) vibration of C=O bond in bidentate
mode. In addition, the peak at 1179 indicates the vibration
band due to C–N stretching and band at 1329 cm-1 corre-
sponds to the C=N moiety. Meanwhile, the low frequency
absorptions at 430–470 cm-1 correspond to the m(M–O)
also suggest that the oxygen atoms from the carboxylate
group are coordinated to metal ions. Furthermore, the axially
1H NMR spectra of the free bases P1 and P2, their Tl(III)
and Sn(IV) complexes and the corresponding axially liga-
ted complexes in CDCl3 are discussed. All complexes
exhibit 1H NMR features characteristic for diamagnetic
compounds. The free-base porphyrins exhibited signal at
-2.73 ppm related to NH protons and disappear in the
corresponding metal derivatives and their axially ligated
derivatives. Free-base porphyrins showed singlet at
8.91–8.93 ppm corresponding to the b-pyrrole hydrogens
and peaks in the region 7.22–7.24 ppm corresponding to
the phenyl hydrogens. In general, NMR is quite informa-
tive for confirming the metallation and axial ligation. The
eight b-pyrrole protons which appear as singlet in metal-
free-base porphyrin appeared as one strong signal sur-
rounded by small satellite peaks in Sn(IV) derivatives [17]
giving confirmation for metallation. Furthermore, the b-
pyrrole protons were downfield shifted in metallopor-
phyrins and in the final complexes containing axial ligands
compared to free-base porphyrins. However, axially ligated
derivatives exhibited signals in the upfield region in the
range 6.00–7.00 ppm due to ring current effect in both
metal complexes. 205Tl NMR spectra of 5-SSATlP1 when
recorded in CDCl3 exhibit a sharp resonance at d
2629.629 ppm which confirms the presence of Tl(III) ion
123

Synthesis, thermoanalytical and spectroscopic characterization of newly synthesized…
Table 2 Important IR absorption bands for the ligand and metal complexes
Compounds m(O–H)/
m(N–H)/
m(C–H) asym/
m(sp3-CH) m(=C–H)
sym
m(C=N)/
m(C–N)/
m(C=C)/
m(C=O) m(M–O)/
cm-1
cm-1
cm-1
cm-1
cm-1
cm-1
cm-1
P2
3317
2958
2962
2962
2962
2960
2962
2852
2850
2843
2842
2850
2845
2922
2926
2923
2922
2924
2900
1350
1333
1328
1326
1348
1355
1184
1184
1178
1179
1255
1253
1558
1552
1513
1511
1534
1529
–
–
TlP2
3523
–
–
–
–
–
–
488
462
472
473
472
5-CSATlP2 3464
5-NSATlP2 3454
1723
1720
–
SnP2
3643
5-CSASnP2 3749
1674
3635
3533
5-NSASnP2 3749
3636
–
2960
2843
2918
1353
1252
1525
1670
473
3544
in the complex. 119Sn NMR spectral signal of the tin
complexes in the range d 500 to -1500 ppm was obtained,
supporting hexacoordination of the tin atom and compa-
rable to values previously published for closely related
compounds. In the absence of salicylate, a single NMR
resonance band is observed for tin, centered at -587 to
-590 ppm relative to tetramethyltin (in CDCl3) [2]. In the
synthesized tin complex 5-NSASnP1, the band is observed
at d -629.462 ppm and hence confirms that both axial
position can be readily displaced by salicylates. These
upfield shifts are expected in the light of the increase in
electron density around the tin center by the coordinated
carboxylate groups of the salicylate.
range of 250–385 °C. This pattern is supported by the DTA
curve with exothermic peak at 384.9 °C. In the last stage,
remaining moiety, i.e., thallium metal undergoes decom-
position with a mass loss of 19.2% and it was compared
with theoretical mass value which was found correct. The
upper decomposition temperatures of the complexes are all
higher than those of the ligands and their metallated
derivatives, which indicate that the stability of the com-
plexes is higher than that of the precursors.
5-CSASnP2
Simultaneous TG and DTA curves for the complex are
recorded and are shown in Fig. 2. Thermal analysis of the
complex 5-CSASnP2 shows that the complex decomposes
through four steps. In the first step, mass loss in the tem-
perature range 100–136 °C is due to the dehydration (loss
of one water molecule). The second step 136–240 °C with
net mass loss of 22.56% corresponded to the elimination of
one axial ligand and one chlorophenyl moiety and is
indicated by the DTA curve at 237.15 °C. The next step
involves the decomposition of 5.04% corresponded to the
elimination of CO2 and Cl species. The third step involves
the decomposition of 34.34% in the temperature range of
355–620 °C corresponded to the three chlorophenyl rings
and C6H5O species. The next step (620°–891°) had a net
mass loss of 10.0% and corresponded to the decomposition
of the two pyrrole rings and then no more mass loss is
observed. The remaining residue mass (26.86%) accounts a
little more than the expected yield of two pyrrole rings and
SnO2 (22.9%) which indicate incomplete decomposition
due to the presence of argon atmosphere.
Thermal decomposition processes of the complexes
5-CSATlP2
The thermal behavior of the synthesized complexes was
studied to establish different decomposition process and to
confirm the proposed stoichiometry. The endo- and
exothermic peaks are observed in DTA curves and are
explained with TG curves. The thermal decomposition of
the complexes takes place in four stages (Fig. 1). The TG
curve reveals that the complexes undergo complete
decomposition up to 800 °C, and the DSC curve shows that
the complex decomposes in four stages at 148, 247.2, 384.9
and 503.7 °C. In the first stage of thermal dehydration of
the complex takes place in between 90 and 200 °C with a
mass loss of 1.7% corresponds to the removal of one water
molecule. In the second stage, mass loss of 66.8% corre-
sponds to the decomposition of axial ligand, the four meso-
phenyl rings and two pyrrole rings, as indicated by the
exothermic peak at 247.2 °C. The third stage corresponds
to the decomposition of two remaining pyrrole rings cor-
responding to the mass loss of 12.5% in the temperature
On comparing the stability of complexes of thallium(III)
and Sn(IV), complexes of later are expected to be more
stable in the selected series of porphyrins. This is disclosed
by the first decomposition temperature of 5-CSASnP2 at
123

S. Katoch et al.
Fig. 1 TG/DTA curve of
5-CSATlP2
148.0°C –1.7%
0
–20
90
80
70
60
50
dM-rel
–40
247.2°C –68.5%
–60
40
30
20
10
0
Exo
Endo
384.9°C –81.0%
–80
Heat flow (smoothed)
503.7°C –100.2%
–100
100
200
300
400
500
600
700
Temperature/°C
240 °C which is higher than the corresponding complex of
thallium.
XRD patterns of the P2, TlP2, SnP2, 5-CSATlP2 and 5-
CSASnP2 with well-defined crystalline peaks indicating
that the complex was amorphous in nature [18]. The
experimental XRD pattern of complexes agrees with the
JCPDS card no. 21-1272 (anatase phase) and the XRD
pattern of rutile phases. The 2h at 25.04°, 37.62°, 46.07°,
57.52° and 61.66° in the XRD pattern of 5-CSASnP2
XRPD analysis
The crystallinity and phase of the product were examined
by powdered XRD analysis. Figures 3 and 4 depict the
Fig. 2 TG/DTA curve of
5-CSASnP2
107.5
100
–21.33
0
136.19°C
99.354%
90
80
70
60
50
40
50
100
237.15°C
76.790%
355.53°C
71.067%
150
200
250
Exo
620.99°C
36.728%
Endo
30
891.68°C
26.861%
300
311.7
21.12
30
100
200
300
400
500
600
700
800
900 950
Temperature/°C
123

Synthesis, thermoanalytical and spectroscopic characterization of newly synthesized…
corresponding to the anatase phase [19], whereas 2h values
at 26.56°, 36.06°, 43.41°, 64.74° and 68.7° corresponding
to the rutile phase with JCPDS card no. 21-1276 [20, 21].
Moreover, careful observation revealed that a systematic
shift to the higher 2h for the diffraction peaks of SnP2 and
5-CSASnP2 as compared to the base compound P2
(Fig. 3a, b). In the final complexes, the slight shift of
diffraction lines toward right when compare with base
compound is due to the metallation and axial ligation. The
diffraction peaks of thallium complexes are little sharper
than the XRD patterns of the tin complexes as a result of
better crystallinity. The crystallite size of the complex
dXRD is estimated from XRD patterns using the Scherre’s
formula:
(c)
(b)
dXRD ¼ 0:9k=bðcos hÞ
dXRD = crystallite
size,
k = X-ray
wavelength
˚
(1.54056 A), b = full width at half maximum (FWHM) of
the diffraction peak (radian), h = diffraction angle at the
peak maximum.
(a)
All the major peaks were used to calculate the aver-
age crystallite size of compounds. The XRD analysis
shows that the P2, TlP2, SnP2, 5-CSATlP2 and
5-CSASnP2 had the average crystallite size of 32.41,
47.61, 35.90, 46.82 and 111.84 nm, respectively, con-
firming the nanocrystalline nature of the complexes. The
observed line broadening in X-ray diffraction lines
agrees well with the crystallite size of the above com-
plexes. Sharper XRD peaks of 5-CSATlP2 (Fig. 4c) are
typically indicative of high nanocrystalline nature and
larger crystallite materials as is confirmed from its
crystallite size calculations.
20
30
40
50
2θ
60
70
80
Fig. 4 PXRD pattern of (a) SnP2, (b) 5-CSASnP2
Fluorescence spectra and lifetime decay
The comparison of the fluorescence spectra resulting from
excitation of the complexes 5-CSASnP2 and 5-CSATlP2
near the Soret bands is shown in Figs. 5 and 6. When
excited at 425 nm, each complex gave a two-banded flu-
orescence spectrum in CH2Cl2. The kem values for tin
complex are in the range of 597–611 (band I) and
650–660 nm (band II) which corresponds to the S1 ? S0
transition and the spectral profile is comparable with hexa-
coordinated tin(IV) porphyrin systems [2]. In thallium
porphyrin complexes, the two emission bands observed at
652–672 and 700–725 nm correspond to the S1 ? S0
transition. Also, there is very weak emission at
647–650 nm which may correspond to the S2 ? S0 tran-
sition. As shown in the figure, the emission bands of tin
porphyrins are less intense than thallium porphyrins which
are attributed to the strong metal–ligand interaction in tin
complexes in contrast to thallium complexes as is usually
observed in case of in-plane porphyrins [22]. The red shift
and the broadening in the fluorescence spectrum of thal-
lium porphyrin complexes in comparison with the tin
complex are due to the distortion of the macrocycles as is
usually observed in SAT porphyrin complexes [23].
(b)
(a)
20
30
40
50
60
70
80
2θ
Fig. 3 PXRD pattern of (a) P2 (b) TlP2, (b) 5-CSATlP2
123

S. Katoch et al.
8
7
Prompt
Decay
Fit
10000
8000
6000
4000
2000
0
Residuals
6
5
4
3
2
1
0
450
500 550 600 650 700 750 800 850
Residuals
400 450 500 550 600 650 700 750 800
Fig. 8 Fluorescence decay and prompt instrumental response with
kexc 425 nm of 5-CSASnP2 in CH2Cl2
Wavelength/nm
Fig. 5 Fluorescence spectra of 5-CSATlP2
The S2-fluorescence decay profiles of 5-CSATlP2 and
5-CSASnP2 are illustrated in Figs. 7 and 8 from which S2-
state lifetimes of 5-CSATlP2 and 5-CSASnP2 were
determined to be 0.44 and 0.55 ns, respectively.
5
4
3
2
1
0
Conclusions
In conclusion, we have synthesized various axially ligated
metalloporphyrins with tin and thallium metals with dif-
ferent axial ligands and are well studied with UV–Vis, IR,
TG, NMR, fluorescence and XRPD results. The optical
absorption spectra reveal very large red shift effects and
broadening of the absorption energies in response to the
substitution of metal and axial ligands. The enhancement
of the optical absorption is most pronounced in the long-
wavelength visible region. Thermal studies of these com-
pounds were performed trying to appreciate the thermal
stability of these compounds and various thermal events of
decompositions. The decomposition temperature of the
respective porphyrins depends upon the metal-porphyrin
bond strength in metalloporphyrins and cleavage of N–H
bond in free-base porphyrin. XRPD studies reveal the
phase and morphology of complexes, and the complexes
are crystallized in mixed anatase, and rutile forms with
well-defined crystalline peaks. What is more, the com-
plexes produce strong characteristic fluorescence. Thus, the
complexes of tin and thallium may be used as optical
materials. The lifetimes of the S2 state of the complexes
obtained confirm previous measurements and permit
accurate evaluations.
450
500
550
600
650
700
750
800
Wavelength/nm
Fig. 6 Fluorescence spectra of 5-CSASnP2
Prompt
Decay
Fit
10000
8000
6000
4000
2000
0
Residuals
400
500
600
700
800
Acknowledgements We would like to acknowledge Indian Institute
of Technology, Mandi, Himachal Pradesh, for photoluminescence
studies and IIIM, Jammu, for their UV–Vis. studies. We thank
University Grant Commission, New Delhi, for their support. We also
thank IISC, Bangalore, for the NMR studies.
Residuals
Fig. 7 Fluorescence decay and prompt instrumental response with
kexc 425 nm of 5-CSATlP2 in CH2Cl2
123

Synthesis, thermoanalytical and spectroscopic characterization of newly synthesized…
13. Valicsek Z, Horvath O, Patonay K. Formation, photophysical and
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